When modeling a complex object, such as a watch, you may choose to model the different parts as separate objects. However, all of the parts may be attached to each other. In these cases, you want to designate one object as the parent of all the children. Movement, rotation or scaling of the parent also affects the children.
To parent objects, select at least two objects, and press Ctrl+P.
A confirmation dialog will pop up asking Make Parent.
Selecting Make Parent confirms and the child/children to parent relationship is created.
The last object selected will be the active object , and will also be the parent object.
If you selected multiple objects before selecting the parent, they will all be children of the parent and will be at the same level of the hierarchy.
Moving and rotating the parent will also usually move/rotate the child/children.
However moving/rotating the child/children of the parent, will not result in the parent moving/rotating.
In other words, influence is usually descendant (parent → child/children),
and not ascendant (child/children → parent).